1. Field of the Invention
The present invention relates to an apparatus for switching and transferring cell signals and frame signals, such as an ATM (asynchronous transfer mode) apparatus and a frame relay apparatus. In particular, the present invention relates to a packet transfer apparatus for efficiently routing cell signals and frame signals that carry packets based on Internet protocols.
There is a requirement for improving the speed of Internet communications made through ATM networks and frame relay networks. IETF (Internet Engineering Task Force), which is a group solving technical problems related to the Internet, and ATM forum, which is a group energetically making ATM specifications and promoting the use of them for ATM-WANs (ATM wide area networks), are studying the standardization of ATM networks and frame relay networks. Such standardization needs intricate, large-scale structures involving address management systems and servers. It is necessary to provide a simple, high-speed communication processing technique.
2. Description of the Related Art
An ATM network or a frame relay network involves routers. The network switches and transfers cell signals or frame signals that carry IP (Internet protocol) packets, and the routers route the packets. The speed of Internet communication in the network is slowed down by inefficient processes carried out between the network and the routers.
FIG. 1A shows a prior art for transferring packet signals in the ATM network, and FIG. 1B shows another prior art for transferring packet signals in the frame relay network.
In FIG. 1A, the ATM network has ATM switches (AS) 11-1 to 11-3 that are provided with routing devices (RD) 10-1 to 10-3, respectively. Each of the routing devices 10-1 to 10-3 has a router for routing a packet signal that carries IP packets.
A source terminal (S) 13 transmits a cell signal made from a packet signal. The cell signal is received by the switch 11-1, which transfers the signal to the routing device 10-1 that is fixedly or semi-fixedly connected to the switch 11-1 through PVC (permanent virtual channel) or SVC (switched virtual channel). The routing device 10-1 reconstructs the packet signal from the received cell signal and determines an outgoing route to a destination terminal (D) 14 according to a destination address contained in the signal.
The routing device 10-1 decomposes the packet signal again into a cell signal having VPI and VCI (virtual path identifier and virtual channel identifier) corresponding to the outgoing route and returns the cell signal to the switch 11-1. According to the VPI and VCI, the switch 11-1 transfers the cell signal to the switch 11-2 that is in the outgoing route. The switches 11-2 and 11-3 and routing devices 10-2 and 10-3 operate in the same way to transfer the signal up to the destination terminal 14.
The prior art of FIG. 1B works in the same manner. The frame relay network has frame relay switches (FR) 12-1 to 12-3 that are provided with routing devices (RD) 10-1 to 10-3, respectively. The routing devices 10-1 to 10-3 route packet signals in the frame relay network. A source terminal (S) 15 transmits a frame signal made from a packet signal. The frame signal is received by the switch 12-1, which transfers the signal to the routing device 10-1 that is fixedly or semi-fixedly connected to the switch 12-1.
The routing device 10-1 reconstructs the packet signal from the frame signal and determines an outgoing route to a destination terminal (D) 16 according to a destination address contained in the packet signal. The routing device 10-1 converts the packet signal again into a frame signal having DLCI (data link connection identifier) corresponding to the outgoing route and returns the signal to the switch 12-1. According to the DLCI, the switch 12-1 transfers the frame signal to the switch 12-2 in the outgoing route.
In this way, the prior art of FIG. 1A must reconstruct and decompose an ATM cell signal at every ATM switch, to increase the transfer time. Although original aims of the ATM technique are to improve a transfer rate and expand a bandwidth, the prior art of FIG. 1A is unable to fully demonstrate the advantages of the ATM technique due to the poor performance of the routing devices.
Similarly, the prior art of FIG. 1B must reconstruct a packet signal and convert it into a frame signal at every frame relay switch, to increase the transfer time. Although original aims of the frame relay technique are to improve a transfer rate and expand a bandwidth, the prior art of FIG. 1B is unable to fully demonstrate the advantages of the frame relay technique due to the poor performance of the routing devices.
In the prior art of FIG. 1B, each frame relay switch must dedicate itself to completely process a received frame. If the transmission rate of a frame signal that carries frames is high, the frame relay switch will be unable to follow the signal, thereby causing congestion in the network.
To solve these problems and improve transfer speed, the IETF has proposed NHRP (next hop resolution protocol), and the ATM forum has proposed MPOA (multiprotocol over ATM).
Each of these proposals employs a shortcut technique that makes a direct connection in a network when transferring IP packets. Making a shortcut, however, involves some problems. For example, it involves intricate control and special protocols that need a client-server system and requires every routing device to have a server function.